The present invention relates to an improved diode laser pumped crystal construction, and, more particularly, to a laser construction having a side pumped laser medium or crystal which has one or more flat surfaces formed thereon and positioned so that when the medium is mounted the flat surfaces are respectively positioned adjacent to reflective surfaces on the mounting means in position to reflect pump energy, including divergent pump energy which otherwise would be lost, back through the crystal so as to increase the amount of pump energy absorbed therein. Some of the reflected energy may be reflected back and forth through the medium more than once. The present construction also includes improved heat dissipation means and improved temperature control means for more effectively and efficiently controlling the operating temperatures of the medium and the pump means. The present construction also facilitates independent temperature control and tuning of the separate laser portions. The separate parts of the present laser can also be manufactured separately which is an important advantage.
With known side pumped laser crystal constructions including known diode pumped laser devices, that energy which is not directed to a predetermined location within the crystal for absorption by the crystal is usually lost, and it is inevitable, especially when utilizing laser diodes as the pump source, that some energy will not be reflected back through the crystal but will be directed at some divergent angles and will pass out through the crystal and be lost. This creates inefficiency and in known lasers this kind of loss has been tolerated. In order to reduce this inefficiency and improve the energy absorption in known devices, more input energy is required and this has increased operating temperatures and caused problems and limitations. This has also led to further increases in the amount of divergent energy and hence has further increased the energy loss and further reduced efficiency. Also, by increasing the input energy, the operating temperature within the crystal increases accordingly which has a further undesirable limiting effect on the operation of the entire device.
One of the closest known prior art constructions is that disclosed in Martin U.S. patent application Ser. No. 100,557, filed Sept. 24, 1987 assigned to Applicants' assignee. This pending application discloses a diode pumped laser device with a laser medium or crystal mounted in a groove formed in a mounting member between spaced and opposed arrays of pumping diodes. Although the device disclosed in the pending application provides novel features and advantages over the known prior art, it does not contain the novel feature of the present device nor does it have the resulting advantages of the present device including reducing the number of arrays of pumping diodes and increasing the energy absorbing efficiency of the system.
The present device, in contrast to known side pumped laser diode constructions, includes distinct and independently controlled sections, including a pump source section and a laser medium or crystal section each of which can be constructed and tuned separately before being assembled. No known diode pumped laser device has the laser medium or crystal and the pump source mounted on different members that may be independently controlled and tuned and which may be separated or disassembled for adjustment, maintenance and tuning. Thus, with the present device, not only are temperature and heat dissipation independently and more effectively controlled, but the laser crystal and pump source may be seperately temperature tuned to respective power supplies. They can also be relatively more easily fabricated, assembled, and disassembled for repair and adjustment.
The independent and more precise temperature tuning and control of the present device provides many advantages. For example, an independently cooled pump source allows for use of a greater variety of pump configurations for the same or different crystals and it permits use with higher power density designs. Also, if the laser gain medium is a Neodymium YAG rod, which rods are known to have relatively poor thermal conductivity, the temperature control of the laser medium using the present device can be operated independently and the laser medium control can be set to provide more active cooling and this will not adversely effect operation of the pump source.
Further, besides providing more efficient temperature control, the laser medium or crystal included in the present device has a novel shape which enables it to be mounted and used to overcome much of the energy loss including loss of the divergent energy which is energy that moves transversely through the medium but at some angle relative to the center or axis of the medium. No known laser device has provision whereby this divergent energy is reflected back and forth through the laser medium to increase the amount of pump energy that is absorbed by the laser medium. This is achieved in the present construction largely by reshaping the crystal medium itself as by forming flat surfaces, generally at right angles to each other on the medium for positioning adjacent to polished surfaces on the mounting mmember therefor. The center of the rod before reshaping to form the flat surfaces as by grinding the medium is also used as the center for energy concentration and absorption after reshaping. The flat surfaces on the modified rod shaped medium enables the medium to be mounted on a shelf portion of the mounting member so that the surfaces of the shelf member which may be formed of material such as polished copper will aid in reflecting the pump energy which impinges thereon back through the medium.
With the present crystal construction, any pump energy that is not absorbed by the laser medium on its first pass through will be reflected by a wall member, and to some extent by the outer flat surface of the medium and this reflected energy will pass back through the medium where some will be absorbed and some will impinge on the opposite cylindrical shaped surface of the medium and some of it will be again reflected back through the medium for increased absorption. That energy which impinges on the cylindrical outer surface of the medium will to some extent be focused by the curved shape of the outer surface toward the center of the medium. Although it is recognized that not all divergent pump energy will be reflected back and forth through the medium, at least some will be and to the extent that this is so it will increase the operating efficiency. It is also preferred that the pump source be a single layer of diodes as this provides for good continuous wave (CW) operation with the cooling provided by the construction.
The fact that with the present construction the lasing medium and the pump source or diode array are mounted on separate mounting members has the further advantage of making it possible to separately manufacture, test and tune the different components, and it also facilitates disassembly of the laser parts for maintenance and other purposes.
It is a principal object of the present invention to provide a diode pumped laser device having a laser medium constructed and mounted so as to reflect some of the diverging pump energy impinging on the medium across the medium in such a way that a greater portion of the total pump energy will be absorbed by the medium.
Another object is to teach the construction of a diode pumped laser having components which are relatively easy to manufacture, test, tune, assemble and disassemble for repair and maintenance.
Another objet is to teach the construction of a diode pumped laser that uses its pump energy more efficiently than known diode pumped lasers.
Another object is to teach the construction and operation of a side pumped laser that requires fewer pump sources.
Another object is to improve the heat dissipation characteristics of diode pumped lasers.
Another object is to teach the construction and operation of a diode pumped laser that has adaquate heat dissipation to enable CW operation.
Another object is to provide improved means for thermal bonding a laser medium to a heat sink.
Another object is to provdde improved means for increasing the energy absorption characteristics of a laser medium by reflecting and focusing the pump energy including diverging pump energy passing through the medium back and forth therethrough.
Another object is to construct a laser that is relatively free of distortion due to flexing or bending of the member supporting the laser components when such member is subjected to substantial heat changes.
Another object is to minimize the possibility for misalignment of the mirrors used in a diode pumped laser device by providing more rigid support means for the laser elements.
Another object is to provide improved means for mounting the mirrors on a laser device.
These and other objects and advantages of the present invention will become apparent after considering the following detailed description of preferred embodiments in conjunction with the accompanying drawings.